date range

def calculate_date_range(input_file, output_file):
    # Read the Excel file with multiple sheets into a dictionary of DataFrames
    dfs = pd.read_excel(input_file, sheet_name=None)
    # Create a new DataFrame to store the observation date ranges
    result_df = pd.DataFrame(columns=['Sheet', 'Min_Observation_Date', 'Max_Observation_Date'])
    # Iterate through each sheet and calculate the date range
    for sheet_name, df in dfs.items():
        if 'observation_date' in df.columns:
            min_date = df['observation_date'].min()
            max_date = df['observation_date'].max()
            result_df = result_df.append({'Sheet': sheet_name, 'Min_Observation_Date': min_date, 'Max_Observation_Date': max_date}, ignore_index=True)
    # Write the result DataFrame to a new Excel file
    with pd.ExcelWriter(output_file, engine='xlsxwriter') as writer:
        result_df.to_excel(writer, sheet_name='ObservationDateRanges', index=False)